1. Field of the Invention
The present invention relates to a large pellicle frame that is a rectangle with a side of greater than 30 cm or a circle with a diameter of greater than 30 cm, and to a large pellicle for lithography comprising the pellicle frame, the large pellicle being used as a dust shield when producing a liquid crystal display plate, etc.
2. Description of the Related Art
In a production process for a liquid crystal display plate, etc., which has been making remarkable progress in recent years, the size of an exposure master plate has been increasing and at the same time the density of a pattern has been increasing. If foreign bodies (particles) become attached to an exposure master plate when the exposure master plate is exposed to light and patterning is carried out, there are the problems that, since the foreign bodies might absorb light or bend the light, the shape of the foreign bodies might be transferred, the pattern might be deformed, an edge might become rough, a white background might become contaminated with black, the dimensions, the quality, the appearance, etc. might be degraded, and the performance of the liquid crystal display plate, etc. and the productivity might be degraded. The ‘exposure master plate’ referred to here means, in addition to an exposure master plate for a liquid crystal display, a photomask for semiconductor use, etc., and includes a reticle and a photomask.
Because of this, these operations are usually carried out in a clean room, but even in a clean room it is difficult to always keep the exposure master plate completely clean. Because of this, a method is carried out that employs a large pellicle in which a pellicle film that is good at letting exposure light pass through is stretched over a pellicle frame so that there is a gap of a few mm between itself and the surface of an exposure master plate, and even if foreign bodies become attached during use they are out of focus and no defects occur in a resist film.
In this case, since foreign bodies are not directly attached to the surface of the exposure master plate but are attached on top of the pellicle, by focusing on the pattern of the exposure master plate during lithography, the foreign bodies on the pellicle do not interfere with transfer. With regard to the pellicle film of the large pellicle, a transparent film formed from nitrocellulose, cellulose acetate, an amorphous fluorine-based resin, etc., which are good at letting light pass through, is used, and the film is bonded via an adhesive such as an acrylic resin or an epoxy resin to an upper part of the pellicle frame, which is formed from aluminum, stainless steel, iron, or another metal (U.S. Pat. No. 4,861,402 and JP-B-63-27707 (JP-B denotes a Japanese examined patent application publication)). Double-sided tape formed from an acrylic-based pressure-sensitive adhesive is usually provided on a lower end face of the pellicle frame as a pressure-sensitive adhesive layer in order to mount an exposure master plate, and a separator for the purpose of protecting the pressure-sensitive adhesion layer is further provided.
In general, a step of affixing the large pellicle to the exposure master plate is as follows.
A separator that protects the pressure-sensitive adhesion layer of the large pellicle is peeled off, and the large pellicle is placed at a pellicle attachment position of the exposure master plate. Subsequently, an attachment jig (jig) that can apply pressure to an outer side of an upper part the pellicle frame is set, and a load is applied via the jig. The attachment jig used here is designed so that a weight is applied to an outer peripheral part of an upper face of the pellicle frame so as to prevent a load from being applied to the pellicle film.
Furthermore, even if a large pellicle attachment system (e.g. M515L (product name) manufactured by Matsushita Seiki Co., Ltd., etc.) is used, when a large pellicle is affixed to an exposure master plate, an attachment jig is used. This attachment jig is identical in principle to that described above, and has a structure such that pressure can be applied to an outer peripheral part of an upper face of a pellicle so as to apply a pressure to an upper face of the pellicle frame without making contact with the pellicle film.
The pellicle affixed to the exposure master plate as described above is used in a lithography step, but when its use is completed or the pellicle film is broken, or when it is contaminated with more than a certain quantity or a certain size of foreign bodies, it is necessary to peel off the pellicle from the exposure master plate.
Since the adhesive strength of the large pellicle is set at a high level compared with one for semiconductor use, it is very difficult to peel off. Furthermore, those currently used are affixed to an exposure master plate via a double-sided tape pressure-sensitive adhesive layer, and when peeled off the pressure-sensitive adhesive layer is swollen by means of an organic solvent, etc. or cut off by means of a cutter knife, etc. so as to remove the pellicle from the plate.
When the large pellicle is removed from the exposure master plate by the above-mentioned method, the surface of the exposure master plate is heavily contaminated, and not only is it necessary to expend effort for subsequent cleaning of the exposure master plate, but it might also become impossible to remove the contamination in some cases and an expensive exposure master plate might become unusable.
As in a laid open patent application (JP-A-9-54424 (JP-A denotes a Japanese unexamined patent application publication)), a method has been proposed in which there is a structure where part of a pressure-sensitive adhesive protrudes outside an outer peripheral part of a pellicle frame, and this part is pulled out in a direction away from the frame when peeling off the pellicle. The present inventors have carried out a variety of investigations into the above-mentioned method using the large pellicle, but when a large pellicle having a high bond strength is used, if the above-mentioned method alone is employed, the pressure-sensitive adhesive breaks, a large amount of glue from the pressure-sensitive adhesive remains on the exposure master plate after peeling off, and good results cannot always be obtained.